<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>canvas实现刮刮卡</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .text {
            position: absolute;
            left: 130px;
            top: 35px;
            z-index: -1;
        }
    </style>
</head>

<body>
    <a href="https://juejin.cn/post/6986785259966857247" style="position: absolute;">代码来源</a>
    <canvas id="canvas" width="400" height="100"></canvas>
    <div class="text">恭喜您获得100w</div>
</body>
<script>
    const canvas = document.getElementById('canvas')
    const ctx = canvas.getContext('2d')

    // 填充的颜色
    ctx.fillStyle = 'darkgray'
    // 填充矩形 fillRect(起始X,起始Y,终点X,终点Y)
    ctx.fillRect(0, 0, 400, 100)
    ctx.fillStyle = '#fff'
    // 绘制填充文字
    ctx.fillText('刮刮卡', 180, 50)

    let isDraw = false
    canvas.onmousedown = function () {
        isDraw = true
    }
    canvas.onmousemove = function (e) {
        if (!isDraw) return
        // 计算鼠标在canvas里的位置
        const x = e.pageX - canvas.offsetLeft
        const y = e.pageY - canvas.offsetTop
        // 设置globalCompositeOperation
        ctx.globalCompositeOperation = 'destination-out'
        // 画圆
        ctx.arc(x, y, 10, 0, 2 * Math.PI)
        // 填充圆形
        ctx.fill()
    }
    canvas.onmouseup = function () {
        isDraw = false
    }
</script>

</html>